Photoelectric registration of ball rotation as teaching aid for ball games

ABSTRACT

The ball is provided with a surface pattern of regions of different optical properties. Light reflected from the moving ball is modulated by the rotation of these regions, transformed into a time variable electrical signal in a photocell, and recorded or displayed.

Inventor Kurt Lehovec l 1 Woodlawn Drive, wlllinmstown, Mass. 01267Appl. No. 801,396

Filed. Feb. 24, 1969 Patented Dec. 28, 1971 PHOTOELECTRIC REGISTRATIONOF BALL ROTATION AS TEACHING AID FORBALL GAMES I [56] References CitedUNITED sTATEs PATENTS 3,274,512 9/1966 Okaya 331 945 3,301,071 1/1967Shalloway 324/70c 1,747,664 2/1930 Droitcomb.... 250/203x 3,486,03212/1969 Cufflin 250/224 3,422,686 1/1969 11111611.... 74/5.6

OTHER REFERENCES 4 Digital Tachometer 8 Claims, 8 Drawing Figs.

Primary Examiner- Ronald L. Wibert LS. Cl; Assislanl Examiner-ConradClark 73/432 lnt.CI G02b27/32,

Golf 15/14 ABSTRACT: The ball is provided with a surface pattern of re-Field of Search 340/220, gi n of different optical properties. Lightreflected from the 420; 250/203;73/432; 356/256, 27;324/28,75, movingball is modulated by the rotation of these regions, 70C transformed intoa time variable electrical signal in a photocell, and recorded ordisplayed.

. l 7 20 l 33. l 27 27 i J t 38 3 39 PATENTEU DEC28|971 SHEET 1 OF 3PATENTEU ntcza I971 SHEET 3 OF 3 E B wk B ES V PHOTOELECTRICREGISTRATION OF BALL ROTATION AS TEACHING AID FOR; BALL GAMES BACKGROUNDOF INVENTION The invention concerns a means for analysis of therotational motion of a ball as a teaching aid for ball games.

Ball games, such as bowling, tennis, baseball and golf are recreationaloccupations enjoyed by millions of persons. Considerable money and timeare invested in mastering the intricacies of these games. In addition tothe direction and speed of the ball delivered bythe player, there isanother elusive quality of the ball, known as a "live" ball in'bowling,a cut" or sliced." ball in tennis, a "curved" ball in baseball, etc.,which refers to the spin imposed on the ball by the player. An objectiveregistration by instruments of this quality considerably aids in theimprovement of the game, by checking the consistency of spin in repeateddeliveries and by enabling the comparison of the chart for the spin ofthe ball of the player with that for the spin of recognized experts ofthe game.

An object of this invention is a means for measurement and registrationof the rotational motion of a ball.

Another object of this invention is a ball provided with a surfacepattern for registration of its rotational motion.

BRIEF DESCRIPTION OF THE INVENTION The device for registration of ballrotation according to this invention utilizes a ball having a surfacepattern of regions'of different optical properties. A photocell isarranged in such a manner that light coming from the ball and strikingthe photocell causes a time variable electrical signal whose intensitydepends on the rotation of the surface pattern of the ball as viewed bythe photocell. By using a multiphotocell arrangement, the ball'rotationcan be resolved into its components of rotation around two perpendicularaxes whose directions are fixed in space, and this suffices to describethe most general mode of rotation of the ball.

EXPLANATION OF DRAWINGS FIG. 1 is a sketch of a sphere forcharacterization of any general rotational motion by rotation aroundtwo. perpendicular axes.

FIG. 2 shows the optical image of aball with a surface pattern accordingto this invention and the preferred arrangement of photocells foranalysis of the ball rotation.

FIG. 3 shows a representation of the photocell outputs for thearrangement of FIG. 2.

FIG. 4 shows an arrangement for keeping the ball image centered withrespect to the photocells.

FIG. 5 shows another arrangement for eliminating the effect of ballimage motion versus the photocells.

FIG. 6 shows a ball according to this invention and the trace of pointson the ball which come successively into the position for reflectinglight into a photocell as the ball rotates.

FIG. 7 is a recording of the photocell output for the case of FIG. 6.

FIG. 8 shows an arrangement for registration of the motion of a bowlingball on an alley according to this invention.

PREFERRED EMBODIMENTS For an understanding of the preferred embodimentsfor analysis of ball rotation, a brief comment on the characterizationof motion of a sphereis helpful.

FIG. 1 shows a sphere I with a point 2 on its surface. A vertical polaraxis 3-3' is shown, and the circle 4 on the surface of the sphere issketched which connects the poles 5, 6, of the axis 33' with the point2. The are between the points 2 and 5 of this circle represents thepolar coordinate 0 of the point 2. The line 7 is the "equator" of thesphere and the intersection of circles 4 and 7 is the point 8. Thehorizontal axis 9-9 is considered to be fixed in space and is used asreference for the longitudinal coordinate 6 of the point 2 as measuredby the arc between the points 8 and 10 along the equator 7. Note thatthe polar coordinate 0 is not changed by rotation of the sphere aroundthe polar axis 3-3'. The point 2 would merely move along the parallelcircle 1 l of constant latitude 0. On the other hand, rotation of thesphere around the axis 99 moves the point 2 along the circle 12, wherebyboth coordinates 0 and d) are changed.

The motion of the point 2 into a different position, such as 13, can beaccomplished as follows: First, a rotation around the axis 9-9 intoposition 14 on the circle 12. The point 14 has the same latitude as 13since both lie on the circle 15 of equal latitude. Secondly, a rotationaround the axis 3-3' which moves the point 14 into the position 13 alongthe circle 15. The two motions have been indicated by arrows. Thus, anyrotational motion of a sphere which moves a point 2 into a differentposition 13 can be characterized by rotations around two axes throughthe center of the sphere, whose directions are fixed in space and whichare perpendicular to each other.

The rotation around these two axes can be measured as follows: Considerthe ball having a surface pattern of regions of different brightnesssuch as a number of equally spaced bright dots on a dull background. Dotpositions in such a regular arrangement are easily derived frompolyhedrons with regular faces: e.g., the comers of a tetrahedronprovide a four-dotpattern; pattern; the corners of an octahedron providea sixdot-pattem and its face centers an eight-dot-pattern; the facecenters of a dodecahedron provide a I2-dot-pattem and its comers a20-dot pattern.

An optical image of a ball having dots arranged in the corners of adodecahedron is shown in FIG. 2. The 15 visible dots of the ball arenumbered 2034. Consider a photocell exposed only to the thinstrip-shaped section between 36 and 37, perhaps by covering up thesection of the image outside the lines 36 and 37, or else by using aphotocell of strip-shaped sensitive area. If the ball rotates aroundhorizontal axis such as 9 9', all the dots on the ball will come intothe view point of the photocell once during each full rotation and thendisappear with the possible exception of at the most two dots whichmight happen to be located at the poles of the axis 9--9'. Thus, witheach full rotation around the axis 9-9, the photocell will provide anumber of electric pulses essentially equal to the number of bright dotson the ball. The number of pulses generated by the photocell can becounted by an electrical counter, taking into account pulses'of extraduration or extra length which might arise from two dots more or lesssimultaneously crossing the. view field of the photocell between 36 and37.

On the other hand, a rotation around the vertical axis 3-3'- will notcause a significant number of pulses in the photocell exposed to thestrip between 36 and 37 since most of the dots do not cross thehorizontal area by rotation around the vertical axis.

In order to measure the rotation around the vertical axis, the photocellshould be positioned to view the vertical strip between the lines 38 and39 in FIG. 2.

Any general rotation can be composed of two rotations around the axes33' and 99' as was shown on hand of FIG. I. A general rotation can thusbe registered by means of two photocells, exposed simultaneously each toone strip, the strips being perpendicular to each other. The result canbe expressed in various manners: FIG. 3 shows a representation of therotational ball motion on an xy chart. Along the ordinate axis y thereis plotted the number of counts registered by the photocell number I,which is exposed to the strip between the lines 36 and 37 in FIG. 2.Along the abscissa axis x, we plotted the number of counts by thephotocell number 2, which is exposed to the strip between the lines 38and 39 in FIG. 2. The number of counts are added electronically for eachphotocell and fed into the x and y inputs of an xy recorder generatingthe trace 90. In regular time intervals, e.g., each 0.2 seconds, amarker signal pulse is impressed on the trace, resulting in the pointsmarked 91-96. If the trace shown in FIG. 3 were that of a bowling ball,and the axis 9-9 of FIG. 2 were horizontal and essentially perpendicularto the trajectory of the ball on the alley, a straight ball, i.e., aball without spin, would have a trace along the ordinate y. Thex-deflection in FIG. 3 thus measures the spin. The fact that the timemarkers 91 and 92 lie closer together than subsequent markers 94 and 95,indicates an initial skidding motion before the ball "grips the alley.

Other representations of the photocell output can be chosen. E.g., thetwo time tracks of the outputs of the two photocells can be displayed oncharts or else registered on magnetic tape for storage and laterdisplay. Still another representation might consist in printing outtotal count numbers for each photocell at various time intervals. Thesenumbers can be evaluated mathematically in a computer to obtain anydesired characterization of the ball motion. For instance, the ballrotation could be described in terms of a rotation at various speedsaround a single axis, the axis shifting its direction slowly with time.

In the arrangement of registration shown in FIG. 2, it is important thatthe ball image is centered with respect to the crossing points of thestrips 36-37 and 38-39. This can be achieved by a tracking mechanism,for which FIG. 4 shows an example. 40-43 are four photocells. 40 and 41measure the light pulse input into a horizontal strip such as betweenthe lines 36 and 37 of FIG. 2 and 42 and 43 achieves the same for thevertical strip such as between the lines 38 and 39 in FIG. 2. If theball is centered with respect to the vertical centerline through 42 and43, the photocells 40 and 41 will display the same signal intensity whenaveraged over time. The timeaveraged outputs of these photocells 40 and41 are fed into a differential amplifier 44 through the wires 45 and 46,and its output is fed into a servomotor 47 through wire 48. Theservomotor moves the four-photocell arrangement along the horizontalaxis 99' to the left or right depending on the polarity of the signalfrom the differential amplifier 44. If the ball image is off center asshown by the circle 49, the photocell 40 will receive a larger timeaverage signal than 41 and the output of the differential amplifier 44causes the servomotor 47 to drive the four-photocell arrangement to theleft as indicated by the arrow until the center position of the ballimage coincides with that of the four photocells.

It is obvious that a similar arrangement can be provided for keeping theball image centered with respect to the axis 9-9 by another differentialamplifier hooked up to the photocells 42 and 43 and feeding a servomotorwhich displaces the fourphotocell arrangement in the vertical 3-3'direction.

A possible arrangement which does not require mechanical motion for 3-ofball image with respect to photocell location is shown in FIG. 5.Several photocells 101-106 of vertical strip shape are positioned in theplane of the ball image at equal lateral intervals. The image of theball 100 encompasses the photocells 102, 103 and 104, but does not fallon the photocells 101, 105 and 106. If the ball image moves into theposition 107, the photocell 102 does not register any more signal pulsesfrom the surface regions of the ball, but the photocell 105 nowregisters such signal pulses, so that the number of output pulses atterminal 108 is not affected since all photocells are connected in aparallel configuration. 109 is a power source and 110 a load resistance.The output 108 can be fed into a pulse counter or connected to arecorder and plotted vs. time.

The same principle can be applied to vertical motion of the ball imageby using a number of vertically equally spaced photocells of thehorizontal strip type.

Instead of using a number of individual photocells connectedelectrically in a parallel arrangement, such as 101 and 106 in FIG. 5,one may use a single photocell of sensitive area large compared to theball image and cover its surface with a diaphragm containing a number ofequally spaced striplike openings corresponding to the areas 101 to 106of FIG. 5.

Analysis of ball rotation can also be achieved by using the light signalreceived by a single photocell from a single point of the ball surface.This condition is realized when using the ball as reflector of lightbeam projected onto the photocell.

Since the curved surface of the ball acts as a dispersive mirror, only avery small surface area, i.e., a "point" on the surface, will contributeto the light reaching the photocell at a given time. No lens system needbe used in principle to form an image of the ball on the photocell,although an optical arrangement can be helpful to increase signalintensity by increasing the point"-area.

FIG. 6 shows a ball 60 having a dot pattern 61, 62, 63 and 64 of brightdot-shaped areas. The lines 50, 51, 52 and 53 are part of a spiralencircling the ball and represent positions on the ball surface whichmove successively into the point from which the photocell receives itssignal as the ball travels along.

If the ball motion is a simple rotation around a single axis whosedirection is fixed in space, the spiral 50-53 would degenerate into asingle circle on the ball surface. The time pattern generated by thephotocell would then be repetitive. However, when the cell motion ismore complex so that it requires the rotations around two axes foradequate description, the curve 50 will not retract itself exactly, anda spiral pattern such as shown in FIG. 6 will arise. As a result, thedot 61 will be crossed along slightly different paths by thetrajectories 50-52. For instance, the trajectory 50 crosses the dot 61close to its circumference; the next trajectory 51 crosses the same dotnear the center; the subsequent trajectory 52 crosses the dot near itsperiphery and the trajectory 53 does not cross the dot 61 at all. Thephotocell signal arising from the dot 61 during the trajectories 50-53will thus consist of three pulses of different widths, as shown in FIG.7.

FIG. 7 represents a recording of the photocell output vs. time. is thebackground signal level of the ball outside the brightly reflecting dots61-64 of FIG. 6. As the trajectory 50 of FIG. 6 crosses dot 61, thesignal 121 arises. The satellite peaks 122 and 123 arise from thesatellite ring 65 around dot 61 in FIG. 6 and serve to identify the dotfrom which the signal is received. The signal 124 arises from thetrajectory 51 and the signal from the trajectory 52.

The rotational mode of the ball can be reconstructed from the widths ofthe pulses resulting from dot 61, in conjunction with the pulsesresulting from the other dots on the ball. The analysis of these pulsesis simplified by using some means of identifying pulses belonging to thesame dot. Such means include dots of different brightness or color; orelse a rim structure code such as a number of narrow circles surroundinga dot, the number of circles differing for different dots. E.g., dot 62has two such satellite circles while 61 has only one. The analysis justdescribed employs preferably a rather small number of large dots whichare distinct from each other in contrast to the method discussed on handof FIGS. 2 and 3 which employs preferably a rather large number ofsmall, identical dots.

FIG. 8 shows a complete arrangement for registration of ball motionaccording to this invention.

Seventy is a bowling alley with the pin positions marked by circles inthe triangular area 71 at one end of the alley and the foul line 72 atthe other end of the alley. 73 is a bowling ball with dot surfacestructures moving along the dashed trajectory 74 toward the pins. Itsprincipal mode of motion is the rotation around the horizontal axis 9-9'through the center of the ball and nearly perpendicular to itstrajectory 74. In front of the foul line, at the right-hand side of thealley, the registration equipment 75 is located, which encompasses thelight projector 76 for illumination of the ball as it moves along thealley; the optical system 77 for producing an image of the ball 73 inthe plane 78 where the photocell or photocells are located and the means79 for photoelectric registration of the ball image as discussedpreviously.

The space taken by equipment 75 has been exaggerated for sake of clarityof representation with respect to the width of the alley. In practice,the projector 76 is preferably arranged above the optical receiver 77 sothat the width of 75 need only be a few inches. Therefore, the equipment75 can be easily placed at the side of the alley so that the approach ofthe bowler for ball delivery is not impeded.

The equipment 75 can be portable and may be shifted along the foul lineto the other side of the alley if so desired in order to avoidinterference with the approach chosen by the bowler. The equipment 75can also be placed in the rear of the alley i.e., near the pin location71.

In the case of ball rotation analysis by a striplike multiphotocellarrangement as discussed on hand of FIG. 2 and FIG. 3, only lateralcentering of the image of the ball is necessary, since the bowling ballmoves along the floor of the alley. In general, centering is minimizedby viewing the ball in the direction of its trajectory 74. If theregistration method discussed on hand of FIG. 6 is used, there is noabsolute need for the lens system 77, although such system might enhancethe photocell signal. The point on the ball surface which reflects theprojected light into the photocell is designated by 80 in FIG. 8. v

The projector may be chosen to emit an infrared or else an ultravioletlight beam in order to avoid distraction of the bowler. Or else, aprojector of visible light may be switched on by a photoelectricarrangement similar to presently existing foul indicators only after theball has been released by the bowler. In general, light projectors ofsuitable spectral distribution or intensity undulation can be used todistinguish the desired signal received by the photocell from the ballfrom background signal, by means of optical or electrical filter andtuning arrangements well known to those skilled in the art.

Surface patterns according to this invention need not necessarilycontain dot-shaped regions; coordinate system such as meridians andlatitude circles of a globe can also be used.

As there are obviously a large number of possible embodiments of myinvention, it should be understood that this invention is not limited bythe preferred embodiments presented, but encompasses all means for ballregistration characterized by the following claims:

1. An apparatus for registration of the rotational component of anunrestricted rotational motion of a substantially spherical body aroundan axis through the center of said body, said axis of direction fixed inspace, said apparatus comprising i. pattern of optically distinctregions on the surface of said body, said pattern consisting ofidentically shaped spots equally spaced across said surface,

ii. means to illuminate said body,

iii. means to project an image of said body on a photocell,

using light reflected from said body,

iv. said photocell exposed only to a portion of said image of said body,said portion being strip-shaped, and oriented parallel to said axis ofdirection fixed in space, and

v. electrical means to count or otherwise record the responses of saidphotocell to the images of said regions as they move through saidstrip-shaped portion due to said rotational component i of motion ofsaid spherical body around said axis.

2. The apparatus of claim 1 including means to keep said image of saidspherical body centered with respect to said strip-shaped exposedportion.

3. The apparatus of claim 1 whereby said strip-shaped portion isnarrower than the spacing between said spots.

4. The apparatus of claim 1 whereby said optically distinct regionsdiffer in color from the background surface of said sphere.

5. The apparatus of claim 1 whereby said optically distinct regionsdiffer in reflectivity from the background surface of said sphere.

6. The apparatus of claim 1 including a second photocell exposed to theimage of a second strip-shaped portion of said spherical body, saidsecond strip-shaped portion orthogonal to said strip-shaped portion ofclaim 21, electrical means to count or otherwise record the responses ofsaid second photocell to the images of said regions as they move throughsaid second strip-shaped portion, whereby the most general rotation ofsaid body is resolved and fully characterized by its rotationalcomponents around said fixed axis of claim 21, and

around a second axis of direction fixed in space, said second axisperpendicular to said axis of clarm 21 and oriented parallel to saidsecond strip-shaped portion.

7. The apparatus of claim 6 including means to center said secondstriplike portion with respect to said spherical body.

8. The apparatus of claim 1 whereby said spherical body is a bowlingball and said axis is chosen substantially perpendicular to the floor ofthe bowling alley.

1. An apparatus for registration of the rotational component of anunrestricted rotational motion of a substantially spherical body aroundan axis through the center oF said body, said axis of direction fixed inspace, said apparatus comprising i. a pattern of optically distinctregions on the surface of said body, said pattern consisting ofidentically shaped spots equally spaced across said surface, ii. meansto illuminate said body, iii. means to project an image of said body ona photocell, using light reflected from said body, iv. said photocellexposed only to a portion of said image of said body, said portion beingstrip-shaped, and oriented parallel to said axis of direction fixed inspace, and v. electrical means to count or otherwise record theresponses of said photocell to the images of said regions as they movethrough said strip-shaped portion due to said rotational component ofmotion of said spherical body around said axis.
 2. The apparatus ofclaim 1 including means to keep said image of said spherical bodycentered with respect to said strip-shaped exposed portion.
 3. Theapparatus of claim 1 whereby said strip-shaped portion is narrower thanthe spacing between said spots.
 4. The apparatus of claim 1 whereby saidoptically distinct regions differ in color from the background surfaceof said sphere.
 5. The apparatus of claim 1 whereby said opticallydistinct regions differ in reflectivity from the background surface ofsaid sphere.
 6. The apparatus of claim 1 including a second photocellexposed to the image of a second strip-shaped portion of said sphericalbody, said second strip-shaped portion orthogonal to said strip-shapedportion of claim 21, electrical means to count or otherwise record theresponses of said second photocell to the images of said regions as theymove through said second strip-shaped portion, whereby the most generalrotation of said body is resolved and fully characterized by itsrotational components around said fixed axis of claim 21, and around asecond axis of direction fixed in space, said second axis perpendicularto said axis of claim 21 and oriented parallel to said secondstrip-shaped portion.
 7. The apparatus of claim 6 including means tocenter said second striplike portion with respect to said sphericalbody.
 8. The apparatus of claim 1 whereby said spherical body is abowling ball and said axis is chosen substantially perpendicular to thefloor of the bowling alley.